High‐Performance Memristors Based on Ultrathin 2D Copper Chalcogenides

Abstract

generally prepared by molecular beam epitaxy (MBE) or wet-chemical methods, have started attracting attention. [11][12][13][14][15][16] However, due to the limitation of their small lateral size, the electronic properties and applications of 2D copper chalcogenides have rarely been touched despite dimensionality plays a crucial role in determining their properties. For example, the quantum confinement effect in reduced dimensionalities is considered to be effective on enhancing the power factor of thermoelectric materials, thereby improving the thermoelectric performance. [17] Thus, a novel synthetic strategy to prepare 2D copper chalcogenides with nanometer thickness and regular structures is needed to be developed.In addition, the small migration barrier of Cu ions, originated from their relatively loose bonding in copper chalcogenides, would result in a low defect formation energy and ubiquitous Cu vacancies. [4,8,18] Considering that ions/defects motion is the basis for resistive switching (RS) devices and related information storage technologies, it is natural to expect a memristive behavior with small switching thresholds in copper chalcogenides, which is highly desired in memristor research since most of 2D memristors own a switching voltage larger than 1 V. [19][20][21][22][23][24] Memristor-based electronics are a mainstream effort to realize low-power artificial intelligence through their analog multiply-accumulate operations in non von Neumann architecture, [25][26][27] and also they can be a promising platform for mimicking the actual biological synaptic connectivity maps. [26] Recently, memristive switching behavior was observed in relatively thick copper sulfide films, and was attributed to the reversible migration of Cu vacancies, [28] an intrinsic nature of copper chalcogenides. As a contrast, the reported 2D memristors mostly require either active metal (such as Cu and Ag) electrodes [24,[29][30][31] or precise control of oxidation to produce extrinsic mobilizable ions/defects/grain boundaries, [23,[32][33][34] which obviously restricts their further applications in an open architecture such as fabricating 2D heterostructures.van der Waals (vdW) epitaxy, which is based on relatively weak vdW interactions between the epitaxial layers and growth substrates, has been proven to be effective in synthesizing 2D planar structures from both layered and nonlayered materials. [3,35,36] In this work, we demonstrate the controllable preparation of a series of 2D binary copper chalcogenideCopper chalcogenides represent a class of materials with unique crystal structures, high electrical conductivity, and earth abundance, and are recognized as promising candidates for next-generation green electronics. However, their 2D structures and the corresponding electronic properties have rarely been touched. Herein, a series of ultrathin copper chalcogenide nanosheets with thicknesses down to two unit cells are successfully synthesized, including layered Cu 2 Te, as well as nonlayered CuSe and Cu 9 S 5 , via van der Wa...

High‐Performance Memristor Based on 2D Layered BiOI Nanosheet for Low‐Power Artificial Optoelectronic Synapses

“…Table 1 shows the comparison of the RS performance, including SET and RESET voltages, ON/OFF ratio, retention time and endurance cycle between our device with other 2D materials‐based memristors. [ 21–37 ] It indicates that our device not only possesses relatively high ON/OFF ratio, but also ultralow SET and RESET voltages when compared with previously published works. Inspiringly, the obtained ultralow SET voltage is one order of magnitude lower than that of most reported memristors based on 2D materials.…”

“…Very recently, ultralow stand‐by power consumption of 5 fW was achieved in 2D layered black phosphorous (BP) nanosheet for memristive devices. [ 33 ] In our experiments, the memristor exhibits low power consumption in the range of <10 pW which is lower than that of most 2D materials‐based memristors, [ 28,29,36,37 ] suggesting promising low‐power applications. Furthermore, we used voltage pulse with pulse width of 1 ms and pulse amplitude of ±1 V to examine the SET and RESET speeds of device.…”

“…The memristor with vertical structure is demonstrated in Process I. When Ag electrode is positively [21] Ag/h-BN/Cu 0.72 −0.37 10 2 3 × 10 3 550 n 2016 [22] Ag/BNO x /graphene 0.7 −0.2 10 3 1.4 × 10 4 100 n 2017 [23] Graphene/MoS 2−x O x / graphene 1.1 −1.5 10 10 5 2 × 10 7 n 2018 [24] Au/Cr/MoS 2 /Cr/Au 1.4 −0.7 10 3 10 4 20 n 2018 [25] Ag/h-BN/graphene 5.2 −4 10 3 n 40 n 2019 [26] Cu/MoS 2 /Au 0.25 −0.15 4 1.8 × 10 3 20 n 2019 [27] Ag/MoS 2 /Pt 0.8 −0.6 10 3 10 5 10 6 7.35 nW 2020 [28] h-rGO/2D CMP/p-rGO/Al 2.9 −2.2 10 3 8 × 10 3 n 2.9 µW 2020 [29] Ti/h-BN/Cu 2.7 −0.86 10 9 10 4 1500 n 2020 [30] Au/Ag/MoS 2 /Si 0.4 −0.3 10 2 2 × 10 4 10 4 n 2020 [31] Ti/PdSe 2 /Au 0.73 −2 10 4 10 6 100 n 2021 [32] Ag/BP/ITO 0.39 −0.37 10 7 10 5 10 4 5 fW 2021 [33] Ti/HfSe x O y /HfSe 2 /Au 2.32 −2.5 10 3 1.5 × 10 4 40 n 2021 [34] Au/Ti/HfSe 2 /Ti/Au/Ti 0.74 −0.81 10 2 10 4 500 n 2021 [35] Au/Ni/MoO x /Mo 2 C/Ni/Au 0.5 −0.3 10 2 n 120 50 nW 2021 [36] Au/Cr/CuSe/Cr/Au 0.4 −0.4 10 2 10 4 300 11.4 µW 2022 [37] Ag/BiOI/Pt 0.05 −0.05 biased during the forming process, oxidized Ag + ions formed at the Ag electrode migrate to the Pt electrode, where Ag + ions are reduced to Ag atoms and then accumulated to grow Ag CFs (Process II), corresponding to the electroforming process. After electroforming, the device is switched from the HRS to the LRS, Ag conductive channel can be formed (Process III).…”

Low-Power Memristor Based on Two-Dimensional Materials

“…For example, owing to the highly active Cu ions with low migration barriers, copper chalcogenides were employed in memristors, demonstrating low V SET (∼0.4 V), fast switching speed (10 μs), stable retention characteristics, and good cyclic endurance performance. 42 For another example, ITO/BP/Ag memristors were fabricated based on naturally oxidated BP which provides a path for coupled ionic−electronic charge transport, and the device demonstrated high on/off ratio (>10 7 ), stable switching cycles (>10 4 ), and a low standby power consumption (<5 fW). 32 Beyond these approaches, integration of different 2D materials to form heterojunction-based memristors is also a feasible way to achieve high performance as well as low power consumption.…”

Atomic Threshold Switch Based on All‐2D Material Heterostructures with Excellent Control Over Filament Growth and Volatility

“…[6] By merging 2D materials into a metal/insulator/metal memristive device, superior non-volatile switching characteristics have been demonstrated. [13][14][15][16] For instance, single-layer hexagonal boron nitride (hBN) shows excellent volatile switching at the quantum level, where B defects strongly influence the formation of conductive Ag filaments. [6] Some previous work has reported an operating current less than picoamperes in an Ag/h-BNO x /graphene device with an atomically thin h-BNO x layer; [17] a low switching voltage of 0.25 V in a Cu/MoS 2 /Au memristor with bi-layer MoS 2 ; [18] and excellent thermal stability up to 340 °C and fast switching in a graphene/MoS 2-x O x /graphene heterostructure.…”